FIG. 1 is an illustration of a conventional light water reactor recirculation pump 10 used to drive coolant/moderator through a nuclear reactor. As shown in FIG. 1, pump 10 includes a shaft 11 that drives a centrifugal or other pump mechanism 19 to create a pressure head or fluid injection into a nuclear reactor. Conventional recirculation pump 10 includes a seal cartridge 12 through which shaft 11 extends. Seal cartridge 12 may generally separate shaft 11 into regions that are immersed in driven fluid, such as at pump mechanism 19, and regions that are dry and receive driving mechanical energy, such as a top portion of shaft 11. A breakdown orifice 13 where shaft 11 passes into seal cartridge 12 may generally prevent or substantially reduce migration of fluid from pump mechanism 19 up along shaft 11 and outside seal cartridge 12. In this way, conventional recirculation pump 10 may drive coolant/moderator through a reactor without loss of coolant/moderator through the pump.
As shown in FIG. 1, some conventional recirculation pumps 10 in pressurized water reactors may include one or more internal organic shutdown seals 15 that may be installed through disassembly of the pump. During non-use of pump 10, such as during maintenance periods or certain transient events like a station blackout, temperatures and pressure of a working fluid through pump mechanism 19 may cause breakdown orifice 13 to leak coolant/moderator. Internal organic shutdown seals 15 may include a separate thermal actuator that releases organic o-rings to permanently seal against and/or adhere to shaft 11 within seal cartridge 12 at a temperature associated with failure of breakdown orifice 13, thereby preventing or reducing leakage along shaft 11 and eventually breakdown orifice 13 caused by temperatures and pressure within the reactor. The organic o-ring may require replacement at time intervals associated with plant outages.